Chemical Characterization of Organic Nanoparticles

Organic aerosol constitutes a major fraction of atmospheric aerosol in the submicron range. Adverse health effects related to particles in this size range as well as their potential impacts on climate have increased the demand for understanding the underlying processes of particle formation and transformation. Besides the direct release of particles through combustion processes, volcano eruptions or sea spray (so-called primary particles), gas-to-particle conversion accounts for the major source of secondary organic aerosol (SOA). Thereby, photo-chemically reacted biogenic precursor gases may lead to particle formation via nucleation and subsequent condensation. The survival rate of nucleated clusters (agglomerates of several molecules in the size range of c.1 nm) to form new particles strongly depends on the growth rate. Understanding and quantifying the growth mechanisms of freshly formed nanoparticles are thus key issues in SOA research. In this project we will employ mass spectrometric techniques to analyze the chemical composition of nanoparticles as small as 10 nm, providing direct insights into the mechanisms and species that control the initial stages of nanoparticle growth. To this end we will conduct complementary laboratory and field studies at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, and a forested field site in the Colorado Rocky Mountains operated by NCAR. In order to reach our goals we choose a comprehensive approach investigating gas-phase, particulate phase and the transition from one to the other simultaneously using various measurement techniques such as gas chromatographs, proton-transfer reaction mass spectrometer, Cluster-CIMS and particle sizers. Particle composition will be measured employing a thermal desorption chemical ionization mass spectrometer (TDCIMS), which is sensitive to aerosol mass loadings in the order of picograms (10-15 kg). We expect to obtain quantitative information on the composition of particles formed from live tree emissions and selected artificial precursor gases representative for the conditions at the field site. By this means we can investigate the feasibility of aerosol growth chambers to simulate SOA formation. The proposed project will contribute to a significant progress in the field of SOA formation, leading to a fundamental understanding of new particle formation and its impact on cloud formation that will reduce the uncertainties associated with aerosol radiative forcing. Societal impacts include closer research ties between the Austrian research community and a world-leading research institute in atmospheric sciences.